Numbers 10:7-9 Revised Standard Version (RSV)
7 But when the assembly is to be gathered together, you shall blow, but you shall not sound an alarm. 8 And the sons of Aaron, the priests, shall blow the trumpets. The trumpets shall be to you for a perpetual statute throughout your generations. 9 And when you go to war in your land against the adversary who oppresses you, then you shall sound an alarm with the trumpets, that you may be remembered before the Lord your God, and you shall be saved from your enemies.